This invention relates to a process for alkylating an alkylatable isoparaffinic hydrocarbon with olefinic hydrocarbons. In another aspect, this invention relates to a process for the alkylation of isoparaffins which employs various energy conservation techniques. In yet another aspect, this invention relates to an alkylation process wherein a prefractionator is used to separate out substantially all of the acid catalyst prior to passing the alkylation zone hydrocarbon to a depropanizer and isostripper. In still another aspect, this invention relates to an alkylation process wherein a propane concentration zone is utilized to increase the concentration of propane in the feed stream to the depropanizer. Still another aspect of this invention relates to the isostripper overhead and bottoms being passed in an indirect heat exchange relationship with feed streams and fractionators in order to supply heat necessary for the preheating or reboiling of said feed streams and fractionators. In still another aspect, this invention relates to an alkylation process which utilizes a fractionation column for raising the propane concentration in the feed stream fed to the depropanizer. In still another aspect, this invention relates to an alkylation process which uses at least one flashing zone to increase the propane concentration in the feed stream to the depropanizer. Still another aspect of this invention relates to the use of the overhead vapor stream from the isostripper as the heat exchange medium for the heating or reboiling of the prefractionation zone in the alkylation process in the use of the bottoms stream of the isostripper as a heat exchange medium to preheat feed stream to the isostripper. Since there is substantially no HF in the feed to the isostripper, this column can then be operated without corrosion problems at relative high pressure and high temperature.
Alkylation of isoparaffinic hydrocarbons with olefinic hydrocarbons is well known as a commerically important method for producing gasoline boiling range hydrocarbons. Generally, the alkylation of isoparaffins with olefins is accomplished by contacting the reactants with an acid-acting catalyst, settling the mixtures to separate the catalyst from hydrocarbons, and further separating the hydrocarbon stream into its various components, i.e., alkylate product. The alkylate is typically a mixture of isomers of heptane, octane, etc., with the exact composition depending upon the isoparaffin and olefin reactants used. Various types of catalysts have been utilized in this reaction, including sulfuric acid, hydrofluoric acid, phosphoric acid, certain halosulfonic acids, and aluminum chloride. The preferred acid catalyst, however, is hydrofluoric acid because of the relative ease with which it can be regenerated and reused and because of the superior quality of the alkylate that is produced.
The energy requirements and costs of an alkylation process can be great and it is therefore desirable to maintain the energy requirements for an alkylation process at a low level. This is particularly important where energy is valuable and the products for generating energy are in relatively short supply and expensive. It has been discovered that by maximizing the use of available waste heat in the system and decreasing the pressure and use of utilities on the depropanizer, that the energy requirements of an alkylation process can be reduced thereby resulting in great energy savings.
Accordingly, it is an object of this invention to provide an improved alkylation process wherein the energy requirements are reduced.
Another object of this invention is to reduce the pressure and utilities on the depropanizer thereby resulting in the energy savings.
Still another object of this invention is to provide an efficient alkylation process which maximizes the possible use of available waste heat in the system.
Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure, the appended claims, and the drawings.